A conventionally known toner supply unit of an image forming apparatus comprises a toner container for withholding toner, a toner transportation path provided between the toner container and a developing unit, and a toner transportation member provided in the toner transportation path, and it is arranged in such a manner that the toner transportation member supplies the toner withheld in the toner container to the developing unit when necessary.
Known as another arrangement of the toner container is a technique disclosed in Japanese Laid-open Patent Application No. 333962/1995 (Tokukaihei No. 7-333962). According to the above publication, the toner container (developer withholding section) is furnished inside with a roller of a developer replenishing member having concavities on its surface, a sealing member for sealing a space between the developer replenishing member and an inner wall of a hopper section, and rotary driving means for rotating the developer replenishing member at a predetermined timing.
In a rotary developing system disclosed in the above publication, the toner container supplies a developing device with the powders of a developer withheld in the hopper section while holding the same in concavities on the surface of the developer supplying member. Also, a space between the developer supplying member and the inner wall of the hopper section is sealed with the sealing member. Moreover, the developer supplying member is arranged to touch the sealing member regardless of an angle at which the developer supplying member is oriented.
Thus, an end of the replenish developer container is always shut off from an end of the developing device with the developer supplying member of the hopper section being provided inbetween. Consequently, the developer is never supplied to the developing device end by natural falling, and powders of the developer are supplied to the developing device end in an adequate quantity by the concavities of the developer supplying member. Thus, this technique is effective in preventing an excessive supply of the developer even when the powders of the developer come to have high fluidity by containing air while the developing device rotates.
A technique disclosed in Japanese Laid-open Patent Application No. 248755/1996 (Tokukaihei No. 8-248755) is known as still another arrangement of the toner container. An image forming apparatus disclosed in the above publication comprises a developing unit and a supplying unit for transporting toner withheld in a toner container by means of a toner transportation member provided in a toner transportation path, and for supplying the toner to the developing unit through a joint portion of the toner transportation path and developing unit, and it is characterized in that an elevated portion is formed in the toner transportation path at the downstream end of a toner transportation route.
Thus, according to the above arrangement, the toner, which has turned into a liquid, will not flow to the downstream end of the toner transportation route from the elevated portion formed in the toner transportation path. Consequently, the toner transportation path can be oriented upward without extending the time required to replenish the toner to the developing unit from the supply unit. In other words, this technique is effective in that the liquid toner is prevented from flowing to the developing unit end with a simple arrangement.
An example adopting a sponge member as the sealing member is disclosed in aforementioned Japanese Laid-open Patent Application No. 333962/1995 (Tokukaihei No. -7-333962). However, it is generally known that the sponge member has very poor durability. Thus, the sealing property is lost as the sponge member deteriorates.
If a rubber member is adopted as the sealing member instead of the sponge member, very high dimensional accuracy is required in the longitudinal direction of the roller of the developer supplying member. Thus, a unit price of each component, and hence a total cost of the apparatus increases undesirably. Further, the flexibility of the rubber member makes is very difficult to seal delicate spaces in the longitudinal direction. Thus, in some cases, the technique disclosed in the above publication can not prevent the flowing of the liquid toner to the developing unit end.
The flowing of the liquid toner to the developing unit end may be prevented by pressing the sealing member hard against the developer supplying member. However, if the sealing member is pressed too hard, the developer supplying member is locked, and the developer may not be supplied in an adequate manner or a load is applied unnecessarily to a driving circuit portion or a driving mechanism portion of the developer supplying member.
Also, in the technique disclosed in aforementioned Japanese Laid-open Patent Application No. 248755/1996 (Tokukaihei No. 8-248755), a space between an exterior of a transportation screw that transports the toner from the hopper and the inside diameter of a transportation pipe is not specifically defined. Thus, it is very difficult to set the space in such a manner that the toner is transported perpendicularly from the transportation screw without causing any leakage, while applying no load on the transportation screw.
In other words, when the exterior of the transportation screw is too large in comparison with the inside diameter of the transportation pipe, a load is applied to the transportation screw, whereas when the exterior is too small, the toner is not transported. Consequently, there arises a problem that a lock phenomenon of the transportation screw occurs or a large quantity of toner is left unused in the hopper.